1
del_client.sh --delete client1 &
del_client.sh --delete client2 &
del_client.sh --delete client3 &
del_client.sh --delete client4 &

When I executed the commands above in the background, client1 was not deleted.

del_client.sh

code which is called during the operation above:

del_client_entry()[

cat $FILE |grep -v ^"${entry}\." | grep -v ^"# ${entry} VT" > $FILE.del
        cp -p $FILE.del $FILE
}
  • 1
    I don't know how $FILE is determined inside the script but it sounds like all 4 invocations of the script might be manipulating the same file at the same time. Since you do not serialize access to the file with a lock, that would explain your result since you would then be facing a race condition. – Celada Mar 28 '16 at 10:42
  • I agree. That's why i am trying to implement locking mechanism. – Gaurav KS Mar 28 '16 at 10:54
  • 1
    You don't show any code that would delete a file, why do you expect one to be deleted? How is $FILE set? How is $entry set? Ho can we know where the error is if you don't show us your script? Please edit your question and give us more information. – terdon Mar 28 '16 at 10:55
4

Your question doesn't say where $FILE gets its value from, but it sounds like every invocation of the script is actually manipulating the same $FILE.

If that's true, then your 4 invocations are racing with each other and the failure you see is expected. Because you carry out a non-atomic read+modify+replace operation on this file and you don't use mutual exclusion to make sure only one process is in its critical section at a time, one of the invocations of the file can easily clobber another's modifications.

You should run del_client_entry under a lock. For example:

(
    flock 9
    del_client_entry <parameters>
) 9>/my/lock/file
  • Initially i was giving same file name, in which i was making changes in /my/lock/file ,so it was not working. Later i gave 9>/tmp/lck, then it worked. Thanks a lot Celada :) – Gaurav KS Mar 29 '16 at 5:13

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